In the manufacture of such coating compositions speed of delivery to customers is an important consideration, but the conventional powder coatings manufacturing method relies on premixing, extrusion and milling as separate processes, causing turnaround times to be long, and production of small batches of a product is not economic. Stocking large product ranges solves the problem of speed of delivery, but is a highly inflexible approach and is not cost-effective.
EP 372860 A describes a colour mixing process for powder coatings in which sufficiently small-sized particles (<20 μm in size and advantageously <10 μm) are used that mixed colours applied to a substrate have a homogeneous appearance. Before application to the substrate the mixture is generally subjected to a process of agglomeration in which the small-sized particles are fused or bonded into composite particles, for example by mechanofusion, to convert the mixture from a cohesive mass to a free-flowing and fluidisable powder, which can be applied by conventional means. Thus, a range of basic coloured powder coating compositions is produced, conventionally, in a conventional melt extrusion step, and the products are comminuted to a distinctively small particle size. A range of other colours can then be produced by mixing and agglomerating these coloured powder bases in the desired proportions. This allows the storage of comparatively few basic coloured powder bases, which can be mixed and agglomerated to produce any desired shade easily on demand, and the production of small quantities becomes commercially feasible.
EP 539385 A describes an extension of this scheme whereby the agglomeration technique is used to incorporate other film-forming or non-film-forming components to produce a range of powder coatings with a range of different performance and aesthetic effects.